Interrogating hot electrons in tunnel junctions

Light impinging on a metal nanostructure can excite plasmons (collective charge-density oscillations), and if plasmons decay into electron-hole pairs, so-called hot carriers can be created (see the figure, top). These hot carriers are produced on a time scale of tens of picoseconds, and their energy distribution differs from that at equilibrium. Potential applications (1, 2) include photochemistry, in which hot electrons can trigger chemical reactions in nearby molecules (3), and in light-harvesting in solar cells (4) and photodetectors (5), in which hot electrons from a metal can overcome the interfacial energy barrier and be injected into a semiconductor. Knowing the hot-carrier energy distribution (HCED) is critical for designing devices or planning reactions. Most studies have been theoretical, with some discrepant results (6–8). On page 423 of this issue, Reddy et al. (9) provide needed direct experimental results on the steady-state energy distribution of hot carriers by cleverly using transmission through molecular resonances.